Hydrocarbon-bearing subterranean formations often contain a number of reservoir compartments physically isolated from one another. Wellbores are often drilled through the subterranean formations to produce hydrocarbons from a number of the reservoir compartments. FIG. 1 illustrates an example of such a system.
In particular, wellbore 110 is disposed through subterranean formation 120. Subterranean formation 120 comprises first reservoir compartment 131 and second reservoir compartment 132. First reservoir compartment 131 is geologically isolated from second reservoir compartment 132 by shale layers 130 such that first reservoir compartment 131 is not in fluid communication with second reservoir compartment 132. Nevertheless, casing 121 of wellbore 110 is perforated in each reservoir compartment 131 and 132 to allow fluid from both first reservoir compartment 131 and second reservoir compartment 132 to mix and produce production output stream 115. Naturally, depending on the conditions (e.g. permeability, porosity, pressure, and temperature) of each reservoir compartment 131 and 132, each reservoir compartment 131 and 132 will contribute a differing quantity of fluids to production output stream 115.
A continuing challenge in the industry is determining the relative contributions of fluid volumes from each of the reservoir compartments 131 and 132 through time. In some cases, mineral rights to each reservoir compartment 131 and 132 may be owned by different entities. In these cases, producers need to know the relative volume contributions from each reservoir to allocate costs and revenue due each owner.
Conventional methods for allocating production between reservoir compartments include mechanical flow meters and chemical tracers. Each of these conventional methods suffers from a variety of significant disadvantages. Mechanical flow meters not only suffer from high installation costs, but also suffer from unacceptable inaccuracies in many cases. In addition to these problems, mechanical flow meters require physical insertion into the wellbore, which results in significant lost production time. Additionally, mechanical flow meters are often difficult to install. In some non-conventional systems where drilling highly deviated wells and horizontal wells are important strategies in production, mechanical flow meters simply cannot be installed or at best struggle to function due to atypical physical configurations of the wellbore systems. In some cases, the mechanical flow meters are only designed to work well over a certain range of flow rates and hence work poorly or not at all outside of their preferred operating ranges.
Occasionally, chemical tracers are employed to allocate production between reservoir compartments. Chemical tracers such as various radioactive isotopes, may be introduced by way of an injection well in communication with one or more of the reservoir compartments. By measuring the amount of tracer in the commingled production stream, one may be able to estimate the relative contribution of fluid volume from one of the reservoir compartments. Due to this method being notoriously unreliable for production allocation purposes, its use to date has been confined mostly to qualitatively determine whether one reservoir compartment is physically isolated from other compartments (e.g. interference determinations). Additionally, the tracer method is extremely expensive, suffering from one of the highest costs of all of the methods for production allocation.
Accordingly, there is a need in the art for improved systems and methods that address one or more disadvantages of the prior art for allocating production between reservoir compartments.